Necropolis versus Academy.

The Necromancer himself is not very useful in the late game because the main problem is gathering enough dark energy. Therefore, if we are not heading towards the Sanctuary, I would take Mentorship. For defense, Reflection is better than Stone Skin. It's also good to take Dark Regeneration, and if there is Dispel, then take Mind Control. You can also develop a secondary hero with Leadership, Herald of Diplomacy, and Abandoned Mines through the mentor. Well, I think that's all.

Actually, no. If the Necromancer's army is much larger than the Academy's army, then instead of Summoning, it's better to take Attack with Tactics, Haste, and Battle Fury.